This invention relates to a microelectrode array for implantation in deep-brain nuclei such as the subthalamic nucleus and the internal segment of the globus pallidus.
Electrical stimulation in deep brain structures (deep brain stimulation, or “DBS”) has developed into an effective treatment modality for advanced Parkinson's Disease and essential tremor. DBS also is being evaluated as a treatment for other neurological conditions and appears to be useful in the treatment of several types of dystonias and hyperkinetic disorders. While the range of clinical applications for DBS has expanded in recent years, its mechanism of action is not completely understood. Studies directed towards an elucidation of the physiologic underpinnings of DBS certainly have been aided by a previously developed microelectrode array for chronic implantation into animals, including subhuman primates, and which delivers highly localized electrical stimulation into the target nucleus, and which includes the capability of monitoring the response to the electrical stimulation by individual neurons in the target nucleus. It is important that the microelectrodes be able to deliver stimulation for an extended interval, and without injury to the tissue. An array of independently controllable stimulating microelectrodes distributed throughout the target nucleus would permit precise control of the spatial distribution of the stimulation, by stimulating either with single microelectrodes or with a subgroup of microelectrodes that could be pulsed either simultaneously or sequentially. This capability is absent in the arrays now in clinical use.
By improving the effectiveness and acceptability of DBS therapy, this technology will improve the quality of life for persons with Parkinson's Disease and other movement disorders. In addition to its applicability in a clinical device, this technology will be valuable in animal models used to investigate the mechanisms by which deep brain stimulation can ameliorate the symptoms of Parkinson's Disease and other movement disorders, and thereby will contribute further to the effective treatment of these disorders.
The previously developed array of microelectrodes, suitable for long-term implantation into the human subthalamic nucleus (STN) or other deep brain nuclei, including the internal segment of the globus pallidus (GPi), is able to record from single neurons in many parts of the target nucleus, can deliver localized microstimulation and localized “sculpted” stimulation at many separate locations within the target nucleus, but also is fully “backward compatible” (can deliver the same maximum stimulus at the same number of sites) as the arrays now in clinical service. Such an array could form the nucleus of a next generation of deep-brain stimulator that would include an adaptive controller that uses the neuronal recordings to adjust the stimulation.
The previously developed array uses 16 discrete activated-iridium microelectrodes. This device can deliver highly localized electrical stimulation within the target, and also can record the action potentials from single neurons, while inducing minimal disruption of the tissues of the target nucleus. The present invention uses new technology to overcome a significant limitation of the previously developed array, namely, its limited number of independent stimulating and recording sites.
The invention is an impovement and extension of the previously developed array of 16 discrete activated-iridium microelectrodes (the Discrete Iridium Array for Deep Brain Microstimulation and Recording, “DIADMAR”). This device can deliver highly localized electrical stimulation within the target, and also can record the action potentials from single neurons, while inducing minimal disruption of the tissues of the target nucleus. The invention uses state-of-the-art technology to overcome a significant limitation of this device for clinical use; namely its limited number of independent stimulating and recording sites. The primary technology used to fabricate the silicon probe (Bosch-process deep reactive ion etching), is known, and has only recently been applied to the fabrication of silicon microprobes. The novel feature of the invention is the manner in which multiple silicon probes will be incorporated into a device that will allow selective and targeted stimulation throughout the recording nucleus, concomitant recording of neuronal activity throughout the nucleus, and full compatibility with the current clinical devices, in a configuration that will induce a minimum of disruption and tissue injury within the target nucleus.
The invention uses an array of multisite silicon-substrate probes which will span the motor portion of the human STN and Gpi. The silicon probes will have mechanical properties suitable for inclusion in an array for clinical use. The number of electrodes sites required to span and populate the human STN or Gpi is too large to be realized using discrete microelectrodes, necessitating the use of multisite silicon probes. The invention uses state-of-the-art micromachining and photolithographic techniques to place a large number of stimulating and recording sites within the target nucleus, while minimizing the amount of tissue displaced and thus minimizing the risk of tissue injury. The array incorporates up to 70 microstimulating and 70 recording electrode sites, for implantation into the human STN or Gpi. Each array will preferably include 6 discrete iridium “minielectrodes” that can safely inject up to 400 nC/phase at 150 Hz. This will ensure that the device is backward compatible with the arrays now in clinical use for DBS. The recording microelectrodes will form the afferent limb of a “smart” (adaptive) stimulator that could automatically fine-tune the stimulus parameters in patients with Parkinson's Disease.